1. Field of the Invention
The present invention relates to an ink ribbon cassette for use in a printing system of an office machine such as typewriters and printers, and more particularly to an ink ribbon cassette which is free from tension variation in ink ribbon, and, therefore free from variation in supply rate of ink being fed to the ink ribbon, and enables the user to use ink (impregnated in an inking roll of the cassette) substantially without making any waste.
2. Description of the Prior Art
Heretofore, it is known to provide, in a printing system of an office machine such typewriters and printers, an ink ribbon cassette having a construction as shown in FIG. 1 so as to permit an ink ribbon housed therein to be used for a long period of time in printing.
More particularly, as shown in FIG. 1, in the above conventional ink ribbon cassette, an inking roll 2 impregnated with ink is housed in a cassette case 1. Also housed in the cassette case 1 is a ribbon-drive roll 3 which is rotatably driven clockwise by a cassette drive shaft of a printer (not shown). On the other hand, in the cassette case 1, a ribbon-driven roll 5 is resiliently pressed against the ribbon-drive roll 3 by means of a compression spring 4, and, therefore the roll 5 is rotatably driven counterclockwise by the ribbon-drive roll 3 through an ink ribbon 6 which is so sandwiched therebetween as to be driven in a direction "A" when the ribbon-drive roll 3 is rotatably driven clockwise.
On the other hand, as is clear from FIG. 1, a tension spring 7 is so housed in the cassette case 1 as to give the ink ribbon 6 a predetermined amount of tension. Consequently, under the influence of such tension of the ink ribbon 6, an ink transfer roll 8 which is movable in a direction L is resiliently pressed against the inking roll 2 slightly deform the inking roll 2. As a result, when the ribbon-drive roll 3 is driven clockwise, the ink transfer roll 8 and the inking roll 2 are rotatably driven clockwise and counterclockwise respectively by the ink ribbon 6, as shown in FIG. 1.
As a result, in printing operation, the thus deformed inking roll 2 releases its ink (impregnated therein) therefrom and transfers it to the ink transfer roll 8 to permit the same 8 to further transfer or supply the ink to the ink ribbon 6.
However, in the conventional ink ribbon cassette having the above construction, since the inking roll 2 is deformed through the ink transfer roll 8 which is urged against the inking roll 2 only under the influence of the tension of the ink ribbon 6 caused by the tension spring 7, a deformation rate of the inking roll 2 depends on variation in tension of the ink ribbon 6, which makes it difficult to keep a supply rate of the ink (being supplied to the ink ribbon 6) constant. Such variation in tension of the ink ribbon 6 tends to increase in printing operation due to damages of the ink ribbon 6 caused in a printing head section of the office machine, which increases variation of the supply rate of ink being supplied to the ink ribbon 6. Consequently, it is very difficult for the conventional ink ribbon cassette to realize a high-quality printing.
In order to resolve the above problem, another conventional ink ribbon cassette has been proposed, which cassette has a construction shown in FIG. 2. In this another conventional ink ribbon cassette, as in the above conventional ink ribbon cassette, the inking roll 2 impregnated with ink is rotatably mounted in the cassette case 1; the ribbon-drive roll 3 is rotatably driven clockwise by a cassette drive shaft of a printer (not shown); the ribbon-driven roll 5 is resiliently pressed against the ribbon-drive roll 3 by means of the compression spring 4 so as to be rotatably driven counterclockwise by the ribbon-drive roll 3 in printing operation; and the ink ribbon 6 is sandwiched between the ribbon-drive 3 and the ribbon-driven 5 roll so as to be driven in a direction "B" when the ribbon-drive roll 3 is driven.
In the printing operation, the inking roll 2 is brought into a pressure contact with the ribbon-drive roll 3 so as to be rotated on its rotary shaft 2a, so that the inking roll 2 is slightly deformed by the ribbon-drive roll 3 while rotatably driven by the ribbon-drive roll 3. The thus deformed inking roll 2 releases the ink impregnated therein, and transfers it to the ribbon-drive roll 3 to enable the ribbon-drive roll 3 to supply the ink to the ink ribbon 6.
As is clear from the above description, in the above another conventional ink ribbon cassette, since the inking roll 2 is deformed only by the ribbon-drive roll 3 but not deformed under the influence of the tension of the ink ribbon 6, there is no fear that the supply rate of the ink being supplied from the inking roll 2 to the ink ribbon 6 varies, depending on variation in tension of the ink ribbon 6.
However, the another conventional ink ribbon cassette is disadvantageous in that only a part of ink impregnated in a surface portion of the inking roll 2 is transferred to the ink ribbon 6 through the ribbon-drive roll 3 so as to be used in printing (in other words, most of ink impregnated in the remaining portion of the inking roll 2 can not be transferred to the ink ribbon 6 through the ribbon-drive roll 3, and, therefore can not be used in printing).